Advertisement

Advertisement

New Scientist Live

Dual asteroid strike hints at chaos in the inner solar system

By Jeff Hecht

(Image&colon; NASA/JPL-Caltech)

SOMETIME between the demise of the dinosaurs and the rise of primates, Earth suffered a one-two punch from two unrelated asteroids. The double whammy could signify chaos in the inner solar system, triggering a cascade of events that perhaps plunged Earth into the recent ice age.

The depth of debris layers shows that the asteroids struck in quick succession – within 20,000 years of each other, around 36 million years ago. A Popagai-sized impact happens just once every 20 million years. So the thinking was that the two rocks were fragments of one larger asteroid.

Advertisement

But when Birger Schmitz of Lund University in Sweden examined sediment from a site in central Italy containing debris from both impacts, he found two distinct types of meteoritic grains. Those from the part of the deposit associated with Popigai were rich in iron; those from the part associated with Chesapeake Bay were iron-poor. So the pair can’t be explained by a single body breakup – they must be from two separate asteroids (Earth and Planetary Science Letters, doi.org/5cb).

It’s even possible that a change in Earth’s own orbit sent the asteroids on their paths. Such a shift might explain why Earth entered an ice age around 35 million years ago&colon; a new orbit meant less energy from the sun.

“The analysis of the grains is very good and convincing,” says David Nesvorny of the Southwest Research Institute, San Antonio, Texas. But some meteorites are simply made of many kinds of rock, he says.

This article appeared in print under the headline “Dual strike hints at chaos in the asteroid belt”